A power conversion device is mounted on the roof or under the floor of an electric railway car to convert electric power obtained from a power contact line and supply electric power to an electric motor or vehicle-installed equipment. The power conversion device has an inverter circuit for output of a desired alternating current power by switching operation of semiconductor elements, a transformer for performing power conversion between a primary side and a secondary side in a state in which the primary side is insulated from the secondary side, and a rectifier circuit for rectification of the output power of the transformer. A main transformer and a high-voltage device box containing a circuit breaker and an arrester are installed under the floor of a railway car as disclosed in Patent Literature 1.